1. Field of the Invention
The present invention relates to a swing bracket which swings a boom and the like right and left while supporting the boom in a construction machine such as an excavator.
2. Description of the Related Art
A background technique of the present invention is described by taking an excavator shown in FIG. 6 as an example.
The excavator includes: a crawler-system lower traveling body 1; an upper slewing body 2 slewably mounted on the crawler-system lower traveling body 1 around an axis O perpendicular to a ground surface; a working attachment 9 attached to the upper slewing body 2 and including a boom 3, an arm 4, a bucket 5, a plurality of hydraulic cylinders, namely, a boom cylinder 6, an arm cylinder 7 and a bucket cylinder 8 which move the boom 3, the arm 4 and the bucket 5, respectively; an operating seat 10 provided on the upper slewing body 2; and a canopy 11 which covers over the operating seat 10. In the present specification, “front and rear” and “right and left” refer to directionality from the viewpoint of an operator seated on the operating seat 10.
The excavator is a swing-type, further including a swing bracket 12 and a swing cylinder 16. The swing bracket 12 is attached to a front part of the upper slewing body 2 so as to be capable of being turned to swung right and left around swing pins 13 as a vertical axis. A base end part of the boom 3, namely, a boom foot, is attached to the swing bracket 12 via a boom foot pin 14, and one end of the boom cylinder 6 is attached to the swing bracket 12 via a boom cylinder pin 15 turnably around a horizontal axis in a right-and-left direction. The swing cylinder 16 turns the swing bracket 12 so as to swing it. The swing cylinder 16 is attached to the swing bracket 12 via a swing cylinder pin 17, turnably around a vertical axis. The whole of the attachment 9 including the boom 3 is thus allowed to be raised and lowered around the boom foot pin 14 and to be swung right and left around the swing pins 13.
The above configurations are disclosed in Japanese Patent Application Laid-open No. 2003-176548 and Japanese Patent Application Laid-open No. 2004-68290.
FIG. 7 to FIG. 10 show a configuration of a conventional swing bracket 12. The swing bracket 12 is formed by molding to have a boom-foot connection portion 18 to which the boom foot is connected, a boom-cylinder connection portion 19 to which the boom cylinder 6 is connected, a swing-cylinder connection portion 20 to which the swing cylinder 16 is connected, and a bracket body 21. The boom-foot connection portion 18, the boom-cylinder connection portion 19, and the swing-cylinder connection portion 20 form an upper end portion, a front portion of a vertically intermediate region, and a lower-end right-side portion of the swing bracket 12, respectively. The bracket body 21 is a portion other than the connection portions 18 to 20, interconnecting adjacent connection portions.
The boom-foot connection portion 18 has a pair of supporting arms 18a and 18b laterally opposed to each other with an interval. The boom-cylinder connection portion 19 has a pair of supporting arms 19a and 19b laterally opposed to each other with an interval. The swing-cylinder connection portion 20 has a pair of supporting arms 20a and 20b vertically opposed to each other with an interval. Each of the supporting arms 18a, 18b, 19a, 19b, 20a, and 20b has a pin hole 22 to which a pin corresponding to the supporting arms is inserted; the pin is the boom foot pin 14, the boom cylinder pin 15, or the swing cylinder pin 17 shown in FIG. 6.
The excavator further includes a swing-bracket attachment portion 23 shown in FIG. 8, to which the swing bracket 12 is attached. The swing-bracket attachment portion 23 protrudes forward from a front end of the upper slewing body 2. The swing-bracket attachment portion 23 has a pair of supporting parts 23a which are located at a front end of the swing-bracket attachment portion 23 and vertically opposed to each other.
On the other hand, the swing bracket 12 has a main connection portion 24 shown in FIG. 8 and FIG. 10. The main connection portion 24 is to be connected to the swing-bracket attachment portion 23, having a pair of upper and lower parts 24a. The supported parts 24a have respective swing pin holes 25. The swing pin 13 shown in FIG. 6 is inserted through the swing pin holes 25 and the pin holes of the supporting parts 23a. The supported parts 24a are thereby coupled to the supporting parts 23a. 
The swing bracket 12 has a reinforcement structure for particularly reinforcing the swing-cylinder connection portion 20 and peripheral parts thereof. This structure includes a vertical rib 26 shown in FIG. 9. The vertical rib 26 has substantially a triangular shape to interconnect an upper surface of the upper-side supporting arm 20a at a basal portion of the swing-cylinder connection portion 20 and a right side surface of the body 21 adjacent to the upper surface, across over the upper surface of the upper-side supporting arm 20a and the right side surface of the body 21.
However, a specific portion of the vertical rib 26, the portion being surrounded by a circle shown by broken lines in FIG. 9, that is, a terminal connected to the upper-side supporting arm 20a and the right side surface of the body 21, can have stress concentration, which may cause destruction at the portion. Besides, the reinforcement by the vertical rib 26 is not sufficiently effective in the lower supporting arm 20b, which may allow the lower supporting arm 20b to be destructed.
As means for avoiding the destruction, there may be one way to increase a thickness of a portion across over both-side supporting arms 20a and 20b out of the basal part of the swing-cylinder connection portion 20 (an ellipse portion shown by shaded lines in FIG. 9, for example) to thereby increase the reinforcement effect while avoiding the above stress concentration. The increase in the thickness, however, involves a significant weight increase, that is, an increase of a few kilograms depending on a case, thus generating difficulty in handling the swing bracket 12 and increasing cost.
Furthermore, decreasing outward protrusion of the both-side supporting arms 20a and 20b to reduce a load applied to the basal portion extremely constrains a right-and-left movement of the swing cylinder 16 shown in FIG. 6 and FIG. 8.